We carried out 3-D simulations of monodisperse particle suspensions subjected to a constant shear rate with the view to investigate the effect of electrical double layers around the particles on apparent suspension viscosities. To this end, expressions for Debye length, zeta potential and ionic strength (pH) of the liquid were incorporated into our in-house lattice Boltzmann code that uses the Immersed Boundary method and includes sub-grid lubrication models. We varied the solids concentration and particle radius, keeping the particle Reynolds number equal to 0.1. We report on results with respect to the effect of pH (in the range 9 through 12) and Debye length on apparent viscosity and spatial suspension structures, particularly at higher solids volume fractions, and on the effect of flow reversals.

Using an immersed boundary-lattice Boltzmann method, we investigated the response of dense granular suspensions to time-varying shear rates and flow reversals. The apparent viscosity and the evolution of particle clusters were analysed. The solids fractions and particle Reynolds numbers varied over the ranges 5% ≤ φv ≤ 47% and 0.11 ≤ Rep ≤ 0.32. The simulations included sub-grid scale corrections for unresolved lubrication forces. The contribution of the tangential lubrication corrections to the shear stress is dominant when φv surpasses 30%. For φv > 35%, increasing shear-thickening is seen with increasing φv. Following a shear reversal, the number of clusters temporarily increases and then decreases to a stable value over the same time scale as the development of the wall shear stress (and apparent viscosity). Simulations with several step changes in the shear rate show the effects of the previous shear history on the viscosity of the suspension.